Hi, apologies for writing so many emails recently. This is a minor spinoff from the "The Curious Case of T6084" email. While digging into it, I keep asking myself if CmmProc’s live registers should match those of the CmmCall that is calling it? Is there any invariant we try to enforce or would want to enforce? - Can the CmmProcs live registers be a strict superset of the corresponding CmmCalls? From the source comments in `compiler/cmm/Cmm.hs`:
Registers live on entry. Note that the set of live registers will be correct in generated C-- code, but not in hand-written C-- code. However, splitAtProcPoints calculates correct liveness information for CmmProcs.
I would assume that this is an invalid case? - Can the CmmProcs live registers be a strict subset of the corresponding CmmCalls? This case however seems to be valid case. However, this makes me wonder if we can, and should(?) propagate the live register info from the CmmProc to the CmmCall so that they match up, and the registers are not kept live at the origin of the CmmCall if they aren’t needed? And as such potentially compute anything to put into the registers the CmmCall considers live, but the CmmProc would ignore anyway? Cheers, Moritz